1. Field of the Invention
The invention relates to floorboards provided with decorative grooves and methods for making such floorboards. The invention is particularly suited for use in mechanical locking systems integrated with the floorboard of the type described and shown, for example, in WO9426999, WO9966151, WO9966152, SE 0100100-7 and SE0100101-5 (owned by Välinge Aluminium AB), but is also usable in optional joint systems which can be used to join floors.
More specifically, the invention relates above all to floors of the type having a core and a decorative surface layer on the upper side of the core.
The present invention is particularly suitable for use in floating floors, which are formed of floorboards which are joined mechanically with a joint system integrated with the floorboard, i.e., mounted at the factory, and are made up of one or more preferably moisture-proof upper layers of decorative laminate or decorative plastic material, an intermediate core of wood-fiber-based material or plastic material and preferably a lower balancing layer on the rear side of the core. The following description of known techniques, problems of known systems and objects and features of the invention will therefore, as non-restrictive examples, be aimed above all at this field of application and in particular laminate flooring formed as rectangular floorboards intended to be mechanically joined on both long sides and short sides. However, it should be emphasized that the invention can be used in optional floorboards with optional joint systems, where the floorboards have a core and at least one surface layer and where these two parts have different decorative properties in the form of color, pattern, structure or the like. The invention can thus also be applicable to, for instance, floors with one or more surface layers of wood.
2. Background of the Invention
Laminate flooring usually consists of a core of a 6–9 mm fiberboard, a 0.2–0.8 mm thick upper decorative surface layer of laminate and a 0.1–0.6 mm thick lower balancing layer of laminate, plastic, paper, or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability, and the balancing layer keeps the board plane when the relative humidity (RH) varies during the year. The floorboards are laid floating, i.e., without gluing, on an existing subfloor which does not have to be completely smooth or plane. Any irregularities are eliminated by means of base material in the form of e.g. board or foam which is placed between the floorboards and the subfloor. Traditional hard floorboards in floating flooring of this type are usually joined by means of glued tongue-and-groove joints (i.e., joints involving a tongue on one floorboard and a tongue groove on an adjoining floorboard) on the long sides and the short sides. When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of one board is introduced into a tongue groove along the joint edge of an adjoining board. The same method is used on the long side as well as on the short side.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical joint systems. These mechanical joint systems lock the boards horizontally and vertically. The mechanical joint systems can be formed by machining the core of the board. Alternatively, parts of the locking system can be formed of a separate material, which is integrated with the floorboard, i.e., joined with the floorboard even in connection with the manufacture thereof.
The main advantages of floating floors with mechanical joint systems are that they can easily and quickly be laid by various combinations of inward angling and snapping-in. They can also easily be taken up again and used once more at a different location. A further advantage of the mechanical joint systems is that the edge portions of the floorboards can be made of materials which need not have good gluing properties. The most common core material is a fiberboard with high density and good stability usually called HDF—High Density Fiberboard. Sometimes also MDF—Medium Density Fiberboard—is used as core. As a rule, these core materials are of high quality and often have an attractive surface which can resist penetration of moisture.
Laminate flooring and also many other floorings with a surface layer of plastic, wood, veneer, cork and the like are made by the surface layer and the balancing layer being applied to a core material. This application may take place by gluing a previously manufactured decorative layer, for instance when the fiberboard is provided with a decorative high pressure laminate which is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature. The currently most common method when making laminate flooring, however, is direct laminating which is based on a more modern principle where both manufacture of the decorative laminate layer and the fastening to the fiberboard take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the board and pressed together under pressure and heat without any gluing.
In addition to these two methods, a number of other methods are used to provide the core with a surface layer. A decorative pattern can be printed on the surface of the core, which is then, for example, coated with a wear layer. The core can also be provided with a surface layer of wood, veneer, decorative paper or plastic sheeting, and these materials can then be coated with a wear layer.
As a rule, the above methods result in a floor element in the form of a large board which is then sawn into, for instance, ten floor panels, which are then machined to floorboards. The above methods can in some cases result in completed floor panels and sawing is then not necessary before the machining to completed floorboards is carried out. Manufacture of individual floor panels usually takes place when the panels have a surface layer of wood or veneer.
In all cases, the above floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and bands mounted, so that the floor panel can be moved at high speed and with great accuracy past a number of milling motors, which are provided with diamond cutting tools or metal cutting tools, which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries can be formed at speeds exceeding 100 m/min and with an accuracy of ±0.02 mm.
Definition of Some Terms
In the following text, the top visible surface of the installed floorboard is called “front side”, while the opposite side of the floorboard, facing the subfloor, is called “rear side”. The sheet-shaped starting material that is used is called “core”. When the core is coated with a surface layer closest to the front side and preferably also a balancing layer closest to the rear side, it forms a semimanufacture which is called a “floor element”. In the case where the “floor element” in a subsequent operation is divided into a plurality of panels, each of the panels are called a “floor panel”. When the floor panels are machined along their edges so as to obtain their final shape with the locking system, they are called “floorboards”. By “surface layer” are meant all layers applied to the core closest to the front side and covering preferably the entire front side of the floorboard. By “decorative surface layer” is meant a layer which is mainly intended to give the floor its decorative appearance. “Wear layer” relates to a layer which is mainly adapted to improve the durability of the front side. In laminate flooring, this layer includes a transparent sheet of paper with an admixture of aluminum oxide which is impregnated with melamine resin. By “reinforcement layer” is meant a layer which is mainly intended to improve the capability of the surface layer of resisting impact and pressure and, in some cases, compensating for the irregularities of the core so that these will not be visible at the surface. In high pressure laminates, this reinforcement layer usually includes brown kraft paper which is impregnated with phenol resin. By “horizontal plane” is meant a plane which extends parallel with the outer part of the surface layer. Immediately juxtaposed upper parts of two neighboring joint edges of two joined floorboards together define a “vertical plane” perpendicular to the horizontal plane.
The outer parts of the floorboard at the edge of the floorboard between the front side and the rear side are called “joint edge”. As a rule, the joint edge has several “joint surfaces” which can be vertical, horizontal, angled, rounded, beveled etc. These joint surfaces exist on different materials, for instance laminate, fiberboard, wood, plastic, metal (especially aluminum) or sealing material. By “joint edge portion” are meant the joint edge of the floorboard and part of the floorboard portions closest to the joint edge. By “decorative joint portion” is generally meant part of the top surface which is intended to resemble a visible joint between, for instance, stone or wood material.
By “joint” or “joint system” are meant coacting connecting means which connect the floorboards vertically and/or horizontally.
The above techniques can be used to manufacture laminate floorings which are highly natural copies of wooden flooring. In recent years, imitations of stones, tiles and the like have become more and more common. In this context, it is tried to manufacture decorative joint portions between stones and tiles which should be as natural as possible. They should have decoration and structure other than those of the stone material and should also be somewhat lower with respect to the horizontal plane to resemble an embedded joint between two stones or tiles. The techniques used to manufacture these decorative joint portions are expensive and do not provide a natural appearance. It should be possible to increase the market for these types of flooring significantly if decorative joint edge portions could be made in a simpler and less expensive manner and with a more natural appearance.
Conventional Techniques and Problems Thereof
When making laminate flooring with decorative and embedded joint portions, the starting material is a decorative paper with printed joint edge portions. This paper is usually impregnated with melamine resin. Uncontrolled swelling takes place in this operation. In the subsequent lamination, the decorative impregnated paper is placed on a core. A transparent wear layer is preferably placed over this decorative paper and then lamination takes place against an embossed metal sheet, in which joint portions are formed which usually have a structure different from that of the remaining part of the metal sheet and where joint portions are designed so that a depression of 0.2 mm can be provided in connection with laminating. The result is a floor element whose front side has an embedded joint pattern corresponding to the intended joint portions between the tiles.
This manufacturing method suffers from a number of problems which are above all related to difficulties in positioning the decorative paper and metal sheets in connection with laminating and the difficulty in positioning floor element and floor panels in the subsequent sawing and machining of the joint edges.
The metal sheet must be positioned with great accuracy relative to the decorative paper. Even if this is carried out with extremely great accuracy, it is not possible to eliminate the uncontrolled swelling in connection with impregnating. This swelling also causes problems in the sawing operation and machining of joint edges. The result of these swelling and positioning problems is that decoration and embossing do not agree with each other and that the decorative embedded joint portions vary between different floorboards, which results in an unnatural appearance.
To counteract these problems, different methods have been used. One method is to limit the format of the floor element so as to thus reduce the maximum deviation in connection with swelling. Special marks are made on the decorative paper which can then be read optically in connection with pressing and sawing. Then the boards are aligned as accurately as possible and individual adjustment of the sawblades can be made for each floor element.
The main disadvantage of this method is high cost, low capacity and extremely great remaining deviation between decoration, embossing and joint edge in the completed floorboard.
It is also difficult to provide a deep depression in high pressure laminate without damaging the decorative paper. Depressing of joint portions in connection with direct lamination results in fibers of the core being compressed. The compressed fibers can later, if moisture penetrates, swell more than normal and cause damage to the joint edge.